Mapping the binding domain of immunoglobulin light chains for Tamm-Horsfall protein

Restrictive usage of monoclonal immunoglobulin λ light chain germline in POEMS syndrome

POEMS syndrome is a rare plasma cell disorder characterized by peripheral neuropathy, monoclonal gammopathy, and high levels of serum vascular endothelial growth factor, the pathogenesis of which remains unclear. A unique feature of this syndrome is that the proliferating monoclonal plasma cells are essentially λ-restricted. Here we determined complete nucleotide sequences of monoclonal immunoglobulin λ light chain (IGL) variable regions in 11 patients with POEMS syndrome. The V-region of the Igλ gene of all 11 patients was restricted to the Vλ1 subfamily. Searching for homologies with IGL germlines revealed that 2 germlines, IGLV1-44*01 (9/11) and IGLV1-40*01 (2/10), were identified, with an average homology of 91.1%. The IGLJ3*02 gene was used in 11 of 11 re-arrangements with an average homology of 92.2%. These data suggest that the highly restricted use of IGL Vλ1 germlines plays an important role in the pathogenesis of POEMS syndrome.

Pathogenesis and treatment of renal failure in multiple myeloma

Renal failure is a frequent complication in patients with multiple myeloma (MM) that causes significant morbidity. In the majority of cases, renal impairment is caused by the accumulation and precipitation of light chains, which form casts in the distal tubules, resulting in renal obstruction. In addition, myeloma light chains are also directly toxic on proximal renal tubules, further adding to renal dysfunction. Adequate hydration, correction of hypercalcemia and hyperuricemia and antimyeloma therapy should be initiated promptly. Recovery of renal function has been reported in a significant proportion of patients treated with conventional chemotherapy, especially when high-dose dexamethasone is also used. Severe renal impairment and large amount of proteinuria are associated with a lower probability of renal recovery. Novel agents, such as thalidomide, bortezomib and lenalidomide, have significant activity in pretreated and untreated MM patients. Although there is limited experience with thalidomide and lenalidomide in patients with renal failure, data suggest that bortezomib may be beneficial in this population. Clinical studies that have included newly diagnosed and refractory patients indicate that bortezomib-based regimens may result in rapid reversal of renal failure in up to 50% of patients and that full doses of bortezomib can be administered without additional toxicity.

Intact protein core structure is essential for protein-binding, mononuclear cell proliferating, and neutrophil phagocytosis-enhancing activities of normal human urinary Tamm-Horsfall glycoprotein

Tamm-Horsfall glycoprotein (THP) is synthesized in the particular sites of renal tubules acting as a defense molecule in the urinary system. In the present study, we found that THP contained high amount of Siaalpha(2,3)Gal/GalNAc, moderate amount of beta(1,4)GlcNAc oligomers and GlcNAc/branched mannose, and low amount of mannose residues, but no Siaalpha(2,6)Gal/GalNAc, in the side-chains of the molecule. THP exhibited high binding affinity with human TNF-alpha, IgG, C1q and BSA, moderate binding affinity with IL-8, and low binding affinity with IL-6 and IFN-gamma. For exploring the role of carbohydrate side-chains and protein core in the protein-binding and cell-stimulating activities, THP was enzyme-digested with carbohydrate-specific [neuraminidase (Nase), beta-galactosidase (Gase)], protein-specific [V8 protease (V8), proteinase K (PaseK)] and glycoconjugate-specific [carboxypeptidase Y (Case), O-sialoglycoprotein endopeptidase (Oase)] degrading enzymes. We found that THP digested with V8, Oase, and PaseK, significantly reduced its protein-binding, mononuclear cell proliferating, and neutrophil phagocytosis-enhancing activities. These results suggest that the intact protein core structure, but not carbohydrate side-chains, is essential for pleotropic functions of THP molecule.

The Uromodulin C744G mutation causes MCKD2 and FJHN in children and adults and may be due to a possible founder effect

Autosomal dominant medullary cystic kidney disease type 2 (MCKD2) is a tubulo-in terstitial nephropathy that causes renal salt wasting, hyperuricemia, gout, and end-stage renal failure in the fifth decade of life. This disorder was described to have an age of onset between the age of 20-30 years or even later. Mutations in the Uromodulin (UMOD) gene were published in patients with familial juvenile hyperuricemic nephropathy (FJHN) and MCKD2. Clinical data and blood samples of 16 affected individuals from 11 different kindreds were collected. Mutational analysis of the UMOD gene was performed by exon polymerase chain reaction (PCR) and direct sequencing. We found the heterozygous C744G (Cys248Trp) mutation, which was originally published by our group, in an additional four kindreds from Europe and Turkey. Age of onset ranged from 3 years to 39 years. The phenotype showed a variety of symptoms such as urinary concentration defect, vesicoureteral reflux, urinary tract infections, hyperuricemia, hypertension, proteinuria, and renal hypoplasia. Haplotype analysis showed cosegragation with the phenotype in all eight affected individuals indicating that the C744G mutation may be due to a founder effect. Moreover, we describe a novel T229G (Cys77Gly) mutation in two affecteds of one kindred. Three of the affected individuals were younger than 10 years at the onset of MCKD2/FJHN. Symptoms include recurrent urinary tract infections compatible with the published phenotype of the Umod knockout mouse model. This emphasizes that MCKD2 is not just a disease of the young adult but is also relevant for children.

Clinical review: specific aspects of acute renal failure in cancer patients

Acute renal failure (ARF) in cancer patients is a dreadful complication that causes substantial morbidity and mortality. Moreover, ARF may preclude optimal cancer treatment by requiring a decrease in chemotherapy dosage or by contraindicating potentially curative treatment. The pathways leading to ARF in cancer patients are common to the development of ARF in other conditions. However, ARF may also develop due to etiologies arising from cancer treatment, such as nephrotoxic chemotherapy agents or the disease itself, including post-renal obstruction, compression or infiltration, and metabolic or immunological mechanisms. This article reviews specific renal disease in cancer patients, providing a comprehensive overview of the causes of ARF in this setting, such as treatment toxicity, acute renal failure in the setting of myeloma or bone marrow transplantation.

Plasmapheresis in nephrology: an update

PURPOSE OF REVIEW

In the past, recommendations for the use of plasmapheresis were based on findings reported from pilot studies or anecdotes. New results from several randomized controlled trials have changed the indications for the use of plasma exchange.

RECENT FINDINGS

A large randomized controlled study of patients with antineutrophil cytoplasmic antibody associated vasculitis showed benefit of plasmapheresis in those with severe renal disease. Patients receiving plasmapheresis compared with methylprednisolone as adjuvant therapy were more likely to be alive and dialysis independent. Plasmapheresis, following publication of a recent randomized controlled trial, should no longer be used for patients with myeloma and acute renal failure. Standard therapy with five to seven plasma exchanges was compared with standard therapy alone. There was no difference in those patients reaching the composite endpoints between the two treatments. New indications include desensitization protocols, using plasmapheresis and intravenous immunoglobulin, which have allowed transplantation across immunological barriers. Highly sensitized patents and ABO incompatible patients compared with their potential donors are now being transplanted with excellent results. Studies still need to be done to assess the best desensitization protocol.

SUMMARY

The use of plasmapheresis requires further validation by randomized clinical trials. Recent published trials should alter practice but further studies are required.

Medullary cystic kidney disease type 1: mutational analysis in 37 genes based on haplotype sharing

Medullary cystic kidney disease type 1 (MCKD1) is an autosomal dominant, tubulo-interstitial nephropathy that causes renal salt wasting and end-stage renal failure in the fourth to seventh decade of life. MCKD1 was localized to chromosome 1q21. We demonstrated haplotype sharing and confirmed the telomeric border by a recombination of D1S2624 in a Belgian kindred. Since the causative gene has been elusive, high resolution haplotype analysis was performed in 16 kindreds. Clinical data and blood samples of 257 individuals (including 75 affected individuals) from 26 different kindreds were collected. Within the defined critical region mutational analysis of 37 genes (374 exons) in 23 MCKD1 patients was performed. In addition, for nine kindreds RT-PCR analysis for the sequenced genes was done to screen for mutations activating cryptic splice sites. We found consistency with the haplotype sharing hypothesis in an additional nine kindreds, detecting three different haplotype subsets shared within a region of 1.19 Mb. Mutational analysis of all 37 positional candidate genes revealed sequence variations in 3 different genes, AK000210, CCT3, and SCAMP3, that were segregating in each affected kindred and were not found in 96 healthy individuals, indicating, that a single responsible gene causing MCKD1 remains elusive. This may point to involvement of different genes within the MCKD1 critical region.

Where disease pathogenesis meets protein formulation: Renal deposition of immunoglobulin aggregates

Aggregation is one of the important issues encountered during the development of immunoglobulin-based drugs. The aim of the current review is to discuss the causes and consequences of immunoglobulin aggregation as well as the relevance of immunoglobulin aggregation to disease pathogenesis. Extracellular deposition of immunoglobulins, either monoclonal light chains or intact polyclonal antibodies, induces renal failure in various nephropathies. The aggregates can present fibrillar or amorphous structures. In this review, factors known to influence protein aggregation, such as the primary structure of the protein, local environment and glycosylation are assessed, as well as the subsequent altered clearance, fibril formation and toxicity. The role of the protein local environment is emphasized. Even if the local environment causes only minor perturbations in the protein structure, these perturbations might be sufficient to trigger aggregate formation. This fact underlines the importance of choosing appropriate formulations for protein drugs. If the formulation provides a slightly destabilizing environment to the protein, the long-term stability of the drug may be compromised by aggregate formation.

Rapamycin worsens renal function and intratubular cast formation in protein overload nephropathy

BACKGROUND

Rapamycin (sirolimus) is associated with functional nephrotoxicity in some patients with nephrotic glomerular diseases but the pathophysiologic mechanisms are not known. This study investigated the effects of rapamycin on renal function and structure in protein overload nephropathy.

METHODS

Rats with protein overload nephropathy [induced by bovine serum albumin (BSA), 2.1 g by daily intraperitoneal injection, day 0 to day 3] received daily intraperitoneal injections of either vehicle [dimethyl sulfoxide (DMSO)], rapamycin (0.2 mg/kg, an inhibitor of mammalian target of rapamycin), or roscovitine (3.5 mg/kg, a small molecule cyclin-dependent kinase inhibitor) (N= 9 each) from day -3 to day 3.

RESULTS

In protein overload nephropathy, rapamycin caused severe acute renal failure and mild hypercholesterolemia (both P < 0.05). Rapamycin dramatically increased intratubular cast formation, and proximal tubular epithelial cells were swollen and engorged with increased cytoplasmic protein droplets. The number of 5-bromo-2'-deoxyuridine (BrdU)-positive tubular epithelial cells increased by more than 20-fold on day 3 in protein overload nephropathy, and this was attenuated by 65% with rapamycin (P < 0.05), whereas roscovitine was ineffective. Rapamycin increased the protein expression of p27(kip1) in tubular epithelial cells, but did not alter D-type cyclin expression or apoptosis.

CONCLUSION

Rapamycin caused a specific pattern of acute renal injury characterized by increased intratubular cast formation in protein overload nephropathy. This could be due to disruption of a potentially important compensatory mechanism in nephrotic glomerular diseases involving tubular epithelial cell protein endocytosis and proliferation.

Renal effects of Tamm-Horsfall protein (uromodulin) deficiency in mice

The Tamm-Horsfall protein (THP; uromodulin), the dominant protein in normal urine, is produced exclusively in the thick ascending limb of Henle's loop. THP mutations are associated with disease; however, the physiological role of THP remains obscure. We generated THP gene-deficient mice (THP −/−) and compared them with wild-type (WT) mice. THP −/− mice displayed anatomically normal kidneys. Steady-state electrolyte handling was not different between strains. Creatinine clearance was 63% lower in THP −/− than in WT mice ( P < 0.05). Sucrose loading induced no changes between strains. However, water deprivation for 24 h decreased urine volume from 58 ± 9 to 28 ± 4 μl·g body wt−1·24 h−1 in WT mice ( P < 0.05), whereas in THP −/− mice this decrease was less pronounced (57 ± 4 to 41 ± 5 μl·g body wt−1·24 h−1; P < 0.05), revealing significant interstrain difference ( P < 0.05). We further used RT-PCR, Northern and Western blotting, and histochemistry to study renal transporters, channels, and regulatory systems under steady-state conditions. We found that major distal transporters were upregulated in THP −/− mice, whereas juxtaglomerular immunoreactive cyclooxygenase-2 (COX-2) and renin mRNA expression were both decreased in THP −/− compared with WT mice. These observations suggest that THP influences transporters in Henle's loop. The decreased COX-2 and renin levels may be related to an altered tubular salt load at the macula densa, whereas the increased expression of distal transporters may reflect compensatory mechanisms. Our data raise the hypothesis that THP plays an important regulatory role in the kidney.

Management of paraproteinemic renal disease

PURPOSE OF REVIEW

Paraproteinemic renal diseases comprise a group of renal disorders that are difficult to manage, in part because of subtleties in the clinical presentation and confusion regarding diagnosis and appropriate therapy. Often, nephrologists make the diagnosis of the underlying plasma cell dyscrasia following renal biopsy. This review seeks to provide a greater understanding of the mechanism of disease and recent approaches to the management of patients who have AL-amyloidosis, monoclonal light-chain and light and heavy-chain deposition disease [termed ML(H)CDD], and cast nephropathy. All three renal lesions are caused by deposition of immunoglobulin light chains. This review seeks to provide a greater understanding of the mechanism of disease and recent approaches to the management of these patients.

RECENT FINDINGS

The immunoglobulin light chain takes the center stage in the pathogenesis of AL-amyloidosis, ML(H)CDD and cast nephropathy. Modifications in the variable domain are responsible for the affinity of the light chain for a given segment of the nephron and the subsequent toxic manifestations. Therapy aimed at eradicating the offending clone of plasma cells that secrete the monoclonal light chain should be beneficial, but this hypothesis lacks confirmation. Four nonrandomized studies have now demonstrated clinical benefit, including return of renal function, of high-dose chemotherapy with autologous stem cell transplantation (HDT/SCT) in the treatment of patients who have AL-amyloidosis or ML(H)CDD.

SUMMARY

While randomized trials are lacking, the data support the clinical efficacy of more aggressive treatments designed to reduce the plasma cell clone responsible for these renal disorders.

Homozygosity for uromodulin disorders: FJHN and MCKD-type 2

BACKGROUND

Autosomal-dominant medullary cystic kidney disease type 2 (MCKD2) and familial juvenile hyperuricemic nephropathy (FJHN) are heritable renal diseases with autosomal-dominant transmission and shared features, including polyuria, progressive renal failure, and abnormal urate handling, which leads to hyperuricemia and gout. Mutations of the UMOD gene, disrupting the tertiary structure of uromodulin, cause MCKD2 and FJHN.

METHODS

Haplotype analysis of a large Spanish family with MCKD was carried out to determinate genetic linkage to MCKD2 locus. Mutation detection was performed by direct sequencing of the UMOD gene. The level of Tamm-Horsfall protein in the urine was measured by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis.

RESULTS

Linkage to MCKD2 locus was demonstrated (LOD score: 4.13), and a known pathogenic uromodulin mutation was found in exon 4, corresponding to Cys255Tyr, disrupting the light chain binding domain of the protein. In this consanguineous family there were three patients homozygous for the C255Y mutation, and multiple heterozygous cases, allowing the MCKD phenotypes associated with one or two mutant alleles to be compared. The homozygous individuals survived to adulthood, although presenting an earlier onset of hyperuricemia and faster progression to end-stage renal disease than heterozygous individuals. Western analysis revealed lower levels of urine THP in one heterozygous patient compared with a normal control patient, both with normal renal function.

CONCLUSION

The study shows that individuals with two UMOD mutations are viable, but they do have more severe disease on average than heterozygotes. This family sheds light on the possible disease mechanism in this disorder.

Protein reabsorption in renal proximal tubule-function and dysfunction in kidney pathophysiology

The endocytic receptors megalin and cubilin are highly expressed in the early parts of the endocytic apparatus of the renal proximal tubule. The two receptors appear to be responsible for the tubular clearance of most proteins filtered in the glomeruli. Since cubilin is a peripheral membrane protein it has no endocytosis signaling sequence. Cubilin binds to megalin and it appears that megalin is responsible for internalization of cubilin and its ligands, in addition to internalizing its own ligands. The importance of the receptors is underscored by the proteinuria observed in megalin-deficient mice, in dogs lacking functional cubilin, and in patients with distinct mutations of the cubilin gene. In this review we focus on the role of megalin- and cubilin-mediated endocytosis in renal pathophysiology. Association between disorders characterized by tubular proteinuria, such as megaloblastic anemia type-1, Dent disease, cystinosis, and Fabry disease and the dysfunction of proximal tubular endocytosis is discussed. The correlation between the high capacity of endocytosis in the proximal tubule and progressive renal disease in overload proteinuria is considered.

Dysproteinemia and the kidney

Dysproteinemia is a clinical state characterized by abnormal, often excessive, synthesis of immunoglobulin (Ig) molecules or subunits. Dysproteinemia results from clonal proliferation of plasma cells or B lymphocytes. The abnormal circulating Ig molecules or subunits (most commonly free light chains) reach the glomerulus via the systemic circulation and are associated with the development of a variety of pathologic lesions within the kidney. Free light chain molecules may pass through the glomerular basement membrane and form casts within distal tubular lumina (myeloma cast nephropathy) or form crystals within the cytoplasm of proximal tubules (light chain Fanconi syndrome). Alternatively, Ig molecules or subunits may form paraprotein tissue deposits and produce an array of pathologic lesions, most commonly amyloidosis and monoclonal Ig deposition disease. The pattern of renal parenchymal disease is determined by the unique properties of the Ig molecule or subunit. Each of the patterns of renal disease is in turn associated with unique, but frequently overlapping, clinical features and outcomes. This review emphasizes the pathologic, clinical, and prognostic differences among the patterns of renal parenchymal disease related to dysproteinemia.

Mutations of the Uromodulin gene in MCKD type 2 patients cluster in exon 4, which encodes three EGF-like domains

BACKGROUND

Autosomal-dominant medullary cystic kidney disease type 2 (MCKD2) is a tubulointerstitial nephropathy that causes renal salt wasting, hyperuricemia, gout, and end-stage renal failure in the fifth decade of life. The chromosomal locus for MCKD2 was localized on chromosome 16p12. Within this chromosomal region, Uromodulin (UMOD) was located as a candidate gene. UMOD encodes the Tamm-Horsfall protein. By sequence analysis, one group formerly excluded UMOD as the disease-causing gene. In contrast, recently, another group described mutations in the UMOD gene as responsible for MCKD2 and familial juvenile hyperuricemic nephropathy (FJHN).

METHODS

Haplotype analysis for linkage to MCKD2 was performed in 25 MCKD families. In the kindreds showing linkage to the MCKD2 locus on chromosome 16p12, mutational analysis of the UMOD gene was performed by exon polymerase chain reaction (PCR) and direct sequencing.

RESULTS

In 19 families, haplotype analysis was compatible with linkage to the MCKD2 locus. All these kindreds were examined for mutations in the UMOD gene. In three different families, three novel heterozygous mutations in the UMOD gene were found and segregated with the phenotype in affected individuals. Mutations were found only in exon 4.

CONCLUSION

We confirm the UMOD gene as the disease-causing gene for MCKD2. All three novel mutations were found in the fourth exon of UMOD, in which all mutations except one (this is located in the neighboring exon 5) published so far are located. These data point to a specific role of exon 4 encoded sequence of UMOD in the generation of the MCKD2 renal phenotype.

Tamm-Horsfall glycoprotein: biology and clinical relevance

Tamm-Horsfall glycoprotein (THP) is the most abundant urinary protein in mammals. Urinary excretion occurs by proteolytic cleavage of the large ectodomain of the glycosyl phosphatidylinositol-anchored counterpart exposed at the luminal cell surface of the thick ascending limb of Henle's loop. We describe the physical-chemical structure of human THP and its biosynthesis and interaction with other proteins and leukocytes. The clinical relevance of THP reported here includes: (1) involvement in the pathogenesis of cast nephropathy, urolithiasis, and tubulointerstitial nephritis; (2) abnormalities in urinary excretion in renal diseases; and (3) the recent finding that familial juvenile hyperuricemic nephropathy and autosomal dominant medullary cystic kidney disease 2 arise from mutations of the THP gene. We critically examine the literature on the physiological role and mechanism(s) that promote urinary excretion of THP. Some lines of research deal with the in vitro immunoregulatory activity of THP, termed uromodulin when isolated from urine of pregnant women. However, an immunoregulatory function in vivo has not yet been established. In the most recent literature, there is renewed interest in the capacity of urinary THP to compete efficiently with urothelial cell receptors, such as uroplakins, in adhering to type 1 fimbriated Escherichia coli. This property supports the notion that abundant THP excretion in urine is promoted in the host by selective pressure to obtain an efficient defense against urinary tract infections caused by uropathogenic bacteria.

Salt-precipitation method does not isolate to homogeneity Tamm-Horsfall glycoprotein from urine of proteinuric patients and pregnant women

OBJECTIVE

Assessment of the degree of purification of Tamm-Horsfall glycoprotein from anomalous urine.

DESIGN AND METHODS

Two methods have been compared: the method of Tamm & Horsfall (T&H method) consisting in the precipitation of THP by the addition to urine of NaCl up to 0.58 mol/L and the filtration of urine through a diatomaceous earth filter (DEF method) in which THP is selectively trapped because of its gelation/aggregation tendency. The purity of THP preparations has been evaluated by SDS-PAGE analysis and Western blotting developed with anti immunoglobulin G (IgG) antibodies and antichorionic gonadotropin antibodies.

RESULTS

All THPs isolated by T&H method from proteinuric patients were contaminated by IgG and one of the five preparations from pregnant women even by chorionic gonadotropin. A smaller or no contamination was found in THPs isolated by DEF method.

CONCLUSIONS

Although albumin is the most abundant protein in the anomalous urine, it never appears in THP preparations. The consistent contamination with IgG of THP prepared by salt precipitation-method might be related to the formation of a stable complex between the two proteins.

Isolation of mouse THP gene promoter and demonstration of its kidney-specific activity in transgenic mice

Tamm-Horsfall protein (THP), the most abundant urinary protein synthesized by the kidney epithelial cells, is believed to play important and diverse roles in the urinary system, including renal water balance, immunosuppression, urinary stone formation, and inhibition of bacterial adhesion. In the present study, we describe the isolation of a 9.3-kb, 5'-region of the mouse THP gene and show the highly conserved nature of its proximal 589-bp, 5'-flanking sequence with that in rats, cattle, and humans. We also demonstrate using the transgenic mouse approach that a 3.0-kb, proximal 5'-flanking sequence is sufficient to drive the kidney-specific expression of a heterologous reporter gene. Within the kidney, transgene expression was confined to the renal tubules that endogenously expressed the THP protein, which suggests specific transgene activity in the thick ascending limb of the loop of Henle and early distal convoluted tubules. Our results establish the kidney- and nephron-segment-specific expression of the mouse THP gene. The availability of the mouse THP gene promoter that functions in vivo should facilitate additional studies of the molecular mechanisms of kidney-specific gene regulation and should provide new molecular tools for better understanding renal physiology and disease through nephron-specific gene targeting.